In the case of elongated components, such as sections, girders, steel welded structures, etc., blasting for the removal of rust, scale, welding slag, etc. generally takes place in a continuous process, in that the components are conveyed on a conveyor means through the blast cabinet and during the conveying movement are blasted by means of centrifugal blast wheels arranged in fixed manner within the cabinet. Much the same occurs for the blasting of metal plates, wires, etc.
The centrifugal blast wheels of a blasting plant always supply the blast medium or abrasive in a specific direction and with a specific blast angle (jet aperture angle). Apart from the speed and particle size of the blast medium, these two parameters are decisive for the quality of the surface treatment. However, the jet must be oriented in such a way that the blast medium does not remain on the component and does not cover as yet unblasted surfaces during the blasting operation, because this would lead to a considerable reduction in the effectiveness of the action of the jet on the covered surfaces. It is therefore known in connection with moving articles (CH 447 864), to position the centrifugal blast wheels in such a way that the blast medium jet strikes the workpiece in sloping manner from the side and therefore the particles are deflected to the side. Use is made of two oppositely directed centrifugal blast wheels, which are pivotably mounted about an axis in such a way that the impact angle and the width of the blast medium cone on impact can be varied, so as in this way to be able to modify the blasting area and so as to be able to effectively deal with workpieces of different widths. Other known mechanisms (DE 442 768, U.S. Pat. Nos. 3,277,608, 2,295,926), have similar aims, with the blast medium jet being narrowable or widenable by plate like deflecting devices.
It is also known in connection with the blasting of wires (DE 18 15 187, 28 51 173, 28 57 609), to focus the blast medium jet onto the wire through deflecting devices acting from either side.
In the case of sections, girders, welded structures and the like having larger cross-sections generally the top and bottom, as well as the lateral faces can be subject to effective blasting treatment in that several centrifugal blast wheels are positioned above and below the conveyor means. Generally the centrifugal blast wheels are positioned in a plane perpendicular to the conveying direction and each centrifugal blast wheel supplies the blast medium jet in this plane under a different angle to the moving component, so as to effectively cover all surfaces. However, it is not possible to blast in a completely satisfactory manner the surface on the leading and trailing face of the component or the top or cover plates located there. In accordance with a not previously published proposal (DE 40 39 621), this deficiency is remedied in that a deflecting device in the form of a wedge is introduced into the blast medium jet and deflects part of the jet in the conveying direction and the other part counter to this direction. With the partial jet directed against the conveying direction it is possible to blast the leading face or the top plate, whereas, the partial jet deflected in the conveying direction blasts the trailing face or top plate of the component. Thus, during blasting the deflecting wedge must twice be moved into the jet. As the deflecting wedge splits up the blast medium jet, there is only a 50% utilization thereof. It is also disadvantageous that the blast medium of the partial jet directed against the conveying direction remains on the workpiece and therefore hinders subsequent action on the surfaces.